Mobile x-ray unit

ABSTRACT

One embodiment of the present disclosure is directed to a mobile X-ray unit. The mobile X-ray unit may include an X-ray applicator for emitting an X-ray beam for irradiating an object. The mobile X-ray unit may further include a phantom-based dosimetry system configured to perform a dosimetry check of the X-ray beam. The phantom-based dosimetry system may include two sets of dose meters, each set being positioned on a surface at a distinct depth. The mobile X-ray unit may also include a dosimetry control unit configured to receive measurements from the two sets of dose meters and determine whether the dosimetry check is passed based on the measurements.

This application is a continuation-in-part of copending U.S. patent application Ser. No. 13/335,830, filed Dec. 22, 2011, which claims the benefit of priority based on U.S. Provisional Patent Application No. 61/426,925, filed Dec. 23, 2010, and Netherlands Patent Application No. 2005899, filed Dec. 22, 2010. All of the priority documents listed above are incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates generally to a mobile X-ray unit. The present disclosure further relates to a method for dosimetry control of an X-ray beam emitted from the mobile X-ray unit.

BACKGROUND OF THE INVENTION

The incidence rate of skin cancer has substantially increased in the last decade of the 20^(th) century. It is appreciated that over 1.3 million new skin cancers are diagnosed annually, which is increasing at a rate of about 5% per year. Increased exposure to the sun without skin protection and a decreased ozone layer are regarded as the main causes of this increase—a problem estimated to be costing over 1 billion Euros in annual medical treatment expenses. Over 80% of skin cancers occur in the head and neck regions with 50% occurring in patients over 60 years of age. It is expected that a portion of the senior population will double in year 2025 compared to the present demographics. Because of the growing incidence of skin cancer and increasing share of the senior population in the overall demographics, much focus has been placed on cancer treatments and cancer treatment logistics.

Non-proliferative cancers, which are defined by substantially superficial lesions, may be treated in different ways. In one example, non-proliferative cancers may be treated surgically. Surgery, may, however, have certain drawbacks, such as, for example, long waiting lists, complications related to post-treatment care, and risk of infection. Alternatively, patients may undergo irradiation using electrons of soft X-rays. Irradiation may have an advantage of being non-invasive and of a short duration (a treatment session may be as short as 2 to 4 minutes). It will be appreciated that usually the integral treatments using radiotherapeutic techniques may require a number of sessions.

Recently, the use of a mobile and portable X-ray unit has been suggested, which may be used inside a hospital radiotherapy department. An embodiment of such portable unit is described in US 2007/0076851. Existing X-ray units include an X-ray source and a filtering device having a plurality of filters rotatably arranged with respect to a focal point of an X-ray tube for changing filtering characteristics on demand. The plurality of filters are arranged in a filtering device, which is transversely arranged with respect to a longitudinal axis of the X-ray tube. Such an arrangement requires an additional step of measuring the X-ray beam so as to deliver the X-ray beam from the X-ray source towards the filter plane.

Existing mobile X-ray units have certain drawbacks. For example, there may be poor control resulting in difficulty delineating between the X-ray beam emitted from the X-ray tube and a treated region on the patient.

SUMMARY OF THE INVENTION

It is an object of the disclosure to provide an improved mobile X-ray unit. In particular, it is an object of the disclosure to provide a mobile X-ray unit having an X-ray beam delivered in a controlled fashion. To this end, the mobile X-ray unit, according to the present disclosure, may include a phantom-based dosimetry system configured to perform an on-line or a real-time dosimetry check of the X-ray beam. The term “phantom,” as used herein, broadly refers to a structure including, for example, a solid structure having skin-like features or a representation of a portion of the human body, for monitoring a radiation dose or exposure. Similarly, the term “phantom-based” refers to the use of a phantom. For example, a “phantom-based dosimetry system” generally refers to a dosimetry system that uses a phantom in conjunction with a dosimetry system such as a film or a suitable dosimetric device (e.g., TLD, an ionization chamber or a semiconductor). The terms ‘mobile’ and ‘portable’ in the context of the present application may be interchanged as these terms equally relate to an easily moved or transported device, for example, a device which may be moved or transported by a single individual.

It may be advantageous to provide a phantom-based dosimetry system so as to provide an efficient method of determining the radiation delivered from the mobile X-ray unit for quality and safety control.

In some embodiments, the phantom-based dosimetry system may include a pre-manufactured, solid, phantom. The phantom may be manufactured from a material corresponding to the dosimetric properties of a human skin. In some embodiments, the phantom may not only correspond to dosimetric properties of a human body, but also may simulate its external shape. For example, the phantom may model a hand, a neck, an ear, a face, a breast, a nose, or any other non-flat surface. This may be beneficial so as to ensure proper treatment planning and treatment delivery. In particular, the phantom may include inserts which may be used during pre-planning dosimetry as well as during treatment. For example, the phantom may include ear and nose inserts for ensuring an electronic equilibrium and a proper dose distribution when these organs are being irradiated. It may be possible to provide phantoms of different shapes, sizes, and/or configurations so as to model both children and adults.

The phantom may be provided with one or more spaces for accommodating a suitable dose meter. It will be appreciated that the dose meter may be, for example, a film, an ionization chamber, or a semiconductor detector. For facilitating film dosimetry, the phantom may be provided with extendable drawers for accommodating one or more film portions at their prescribed dwell positions. For the ionization chamber and the semiconductor device, the phantom may include dedicated cavities fit to the dimensions of a dose meter to be used.

In one embodiment, the dosimetry system may be connected to a receptacle of an X-ray applicator of the mobile X-ray unit. Although it is contemplated that the dosimetry system may be connected to an independent receptacle, the dosimetry system may also be connected to a collimator receptacle. When the dosimetry system is connected to a collimator receptacle, the phantom-based dosimetry system may be provided with similar attachment structures as the collimators (e.g., pins or plugs) for connecting to the collimator receptacle.

In various embodiments of the present disclosure, the dosimetry system may include a digital read out unit. It may be advantageous to provide an on-line and/or real-time dosimetry system capable of direct data transfer to a suitable data processing unit, which may be in electronic communication with the control unit of the mobile X-ray unit.

In various embodiments of the present disclosure, the dosimetry system may be configured to verify at least a percentage depth dose, a beam flatness, and a dose rate the of generated X-ray field.

It will be appreciated that different embodiments are contemplated. In one embodiment, it may be possible to dispose a dosimetric film sensitive to the X-rays generated by the X-ray tube in a direction that substantially coincides with a longitudinal axis of the emitted X-ray beam. In this manner, a percentage depth dose may be measured. It will be appreciated that one or more such films may be possible to enable off-center measurements.

In another embodiment, it may be possible to provide a number of thermoluminiscent dosimeters (TLD) inside the phantom at pre-determined depths. The TLDs may be aligned with a central axis of the X-ray field, and, additionally, some TLDs may be positioned at off-center locations. The irradiated TLD's may be read out by a dedicated read-out unit, and the data may be made available for further analysis. For example, the TLD reader may export a computer file into a suitable data processing unit.

In another embodiment, the phantom may be provided with one or more cavities for accommodating one or more ionization chambers or one or more semiconductor devices. Such dose meters may be connected to a measurement unit capable of provided on-line dosimetry data. A signal from the measurement unit may be supplied to the control unit of the mobile X-ray unit for recording the dosimetry data and/or for adjusting settings of a high voltage power supply, if necessary. It will be appreciated that a set of miniature ionization chambers may be used.

In some embodiments of the present disclosure, a dosimetry system may have a plurality of dose meters located at different depths, including a first set positioned at the surface of the phantom-dosimetry system and a second set positioned at a depth of 5 mm. It will be appreciated that individual dose meters from the second set may be positioned outside the shadow of the dose meters from the first set. In one embodiment, 10-15 dose meters may be provided at the depth of 5 mm and 10-15 dose meters may be provided at the depth of 10 mm, in a position away from the shadow of the higher dose meters. It will be appreciated that any number of dose meters may be provided at the first depth and the second depth. In some embodiments, such a dosimetry system may be used for performing a daily quality check of radiation dose, dose profile, and timing. For example, changes in surface dose rate and percentage depth dose, and flatness changes may be determined during a quality check procedure based on measurements made by the dose meters.

In various embodiments of the present disclosure, the dosimetry system may be calibrated to determine the absolute percentage depth dose. It may be advantageous when the phantom-based dosimetry system is capable of delivering absolute dosimetry data on-line or in real-time. Those skilled in the art will readily appreciate which calibration measures may be necessary in order to determine an absolute calibration of a dosimetric film, an ionization chamber, or a semiconductor detector. In some other embodiments, the dosimetry system may also determine the relative percentage depth dose, e.g., changes in the percentage depth dose.

In various embodiments of the present disclosure, a surface of the phantom may be provided with an alignment pattern.

It may be advantageous to provide a suitable alignment pattern on a surface and/or inside the phantom. It will be appreciated that to enable visualization of the internal pattern, the phantom material must be substantially transparent. It will be further appreciated that the alignment pattern may also be used to determine if an expected X-ray field, fully or partially visualized using a light indicator, corresponds to the actual X-ray field. In some embodiments, the determination may account for different angulations of the X-ray applicator.

The dosimetry system, i.e. a film or a suitable device (TLD, an ionization chamber or a semiconductor), may include a plurality of measuring points, preferably distributed in a plane. When the dosimetry system is positioned in the X-ray field, the readings may be processed so as to determine the dose data across the applied field. For example, a reading at the central axis may be taken and a number of peripheral readings, preferably at different radial distances. As a result, information may be obtained regarding not only the absolute dose in the central field, but also information about beam flatness across the field. It will be appreciated that for such purposes film dosimetry may be used.

In various embodiments, the X-ray applicator may include an indicator for visualizing at least a portion of the X-ray beam emitting from the exit surface of the applicator.

Treatment efficacy may be substantially improved when an indicator is provided for delineating at least a portion of the generated X-ray beam, like a central axis thereof, and/or a partial or a full beam geometry. In particular, an indicator may be advantageous for positioning the dosimetry system with respect to the X-ray beam. In an exemplary embodiment, the indicator is a light source. The light source may be arranged in the X-ray applicator or, alternatively, the light source may be arranged around an outer surface of the X-ray applicator. When the light source is arranged in the X-ray applicator, the light source may be configured to delineate the central axis of the X-ray beam and/or the full beam geometry. When the light source is arranged around the outer surface of the X-ray applicator, the light source may be arranged to delineate a central axis of the X-ray beam, preferably at a pre-determined distance from the X-ray applicator. This may be advantageous when the X-ray applicator is used at a standard distance from the patient's skin. However, it will be appreciated that the light source arranged around the X-ray applicator may be adjusted so as to indicate the central axis of the X-ray beam at a variety of axial distances from the X-ray applicator.

In various embodiments, the indicator includes an array of light sources concentrically arranged around the X-ray applicator. Although it may be sufficient to provide a single light source that generates a narrow beam for indicating the central axis of the X-ray beam, it may be advantageous to provide a plurality of light sources each of which generates a narrow light beam. These light beams may intersect at a given distance from the lower surface of the X-ray applicator. In this manner, the X-ray applicator may be positioned at a prescribed distance from the skin. Additionally, the phantom-based dosimetry system may be positioned with respect to the X-ray beam. In order to ensure a correct coverage of an object (e.g., phantom-based dosimetry system or target region on a surface of a patient) by the X-ray beam, the X-ray applicator may be positioned so that the indicated center of the X-ray beam is positioned substantially at a center of the object. It will be appreciated that these embodiments function particularly well for regular shaped X-ray beams, for example, when a circular, a square, an elliptic, or a triangular collimator is used for shaping the X-ray beam.

In various embodiments, the light source may be disposed inside the X-ray applicator for generating a light beam configured to be intercepted by a collimator for providing a light image of the X-ray field emitted from the exit window.

This embodiment may be advantageous when the full shape of the X-ray beam is to be delineated such as, for example, in situations when an irregular beam shape is used. In such cases, the light source may be provided near the target region or, via a mirror, off-axis, for generating a light beam configured to be intercepted by the collimator. It will be appreciated that a direction of propagation of the light beam must essentially conform to a direction of propagation of the X-ray beam. In one embodiment, when a mirror is used, the light source may advantageously be positioned off-axis minimizing its radiation damage.

In various embodiments, the indicator includes a light source and an optical fiber configured to deliver light from the light source for interception by the collimator.

This may be advantageous as the light source may be positioned outside the X-ray applicator in order maintain the overall size of the X-ray applicator. For example, the light source may be arranged in the base of the X-ray unit and the optical fibers may run from the base to inside the X-ray applicator for suitably illuminating the collimator for obtaining a light image equivalent to that of the generated X-ray beam.

In various embodiment of the present disclosure, the indicator may include a plurality of optical fibers distributed in the X-ray applicator in an area above the collimator for illuminating a collimator opening to generate a light image of the X-ray field. This embodiment may be advantageous for obtaining a light field having substantial intensity.

In various embodiments, the indicator may include a light source emitting a narrow light beam arranged inside the applicator for delineating a longitudinal axis of the X-ray beam. Preferably, a miniature laser source may be used.

In various embodiments, the mobile X-ray unit may include a radiation detector, which may be provided inside the outer housing for detecting the X-ray beam.

It may be advantageous to provide an independent mechanism for detecting the presence of an X-ray beam. In some embodiments, the X-ray unit includes a primary timer which may set a time for the high voltage supply to deliver a predetermined radiation dose. The radiation detector disposed inside the outer housing of the X-ray applicator may be part of a secondary timer circuit adapted to shut down the high voltage supply when the predetermined radiation dose has been delivered. In this way radiation safety control may be improved.

In some embodiments, in which a dosimetry system may provide data in real-time, the signal from the dosimetry system may be used in addition to the signal from the built in radiation detector. In particular, when the dosimetry system is arranged to verify the beam characteristic, a substantial deviation from the prescribed beam flatness may be used as a control signal to shut-down the mobile X-ray unit.

Another embodiment of the present disclosure is directed to a method for dosimetry control of an X-ray beam emitted from a mobile X-ray unit. The mobile X-ray unit includes a base for accommodating a control unit configured to control an X-ray applicator and a power supply a power supply. The mobile X-ray unit further includes an articulated arm supporting an X-ray applicator having an X-ray tube for generating an X-ray beam. The method includes providing a phantom-based dosimetry system for verifying at least a percentage depth dose of the X-ray beam.

In some embodiments, a solid phantom may be provided with one or more dose meters for checking percentage depth dose, beam flatness, and the dose rate that is used. The phantom may be manufactured from a material corresponding to dosimetric properties of human skin. In one embodiment, the phantom is humanoid, simulating an outer surface of a portion of a human body, such as, for example, an ear, a hand, a nose, a breast, a neck, or any other portion of the human body.

In various embodiments of the present disclosure, an indicator may be provided in or near the X-ray applicator for visually delineating at least a portion of the X-ray beam for positioning the phantom-based dosimetry system. In some embodiments, the indicator may include a light source arranged to generate a light field configured to be intercepted by a collimator opening for providing visualization of the X-ray beam. Alternatively, the indicator may include a light source arranged to delineate a longitudinal axis of the X-ray beam.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a presents a perspective view of a mobile X-ray unit, according to embodiments of the present disclosure.

FIG. 1 b presents a partial perspective view of a mobile X-ray unit illustrating movement of a displaceable panel, according to embodiments of the present disclosure.

FIG. 1 c presents a schematic view of the mobile X-ray unit shown in FIGS. 1 a and 1 b, illustrating displacement of an X-ray applicator of the X-ray unit relative to a base of the mobile X-ray unit, according to embodiments of the present disclosure.

FIG. 2 presents a diagrammatic representation of the mobile X-ray unit, according to embodiments of the present disclosure.

FIG. 3 presents a schematic view of a dosimetry system of the X-ray unit according to the invention.

FIG. 4 a presents a cross-sectional view of an X-ray applicator of the mobile X-ray unit having an indicator, according to a first embodiment of the present disclosure.

FIG. 4 b presents a cross-sectional view of an X-ray applicator of the mobile X-ray unit having an indicator, according to a second embodiment of the present disclosure.

FIG. 4 c presents a cross-sectional view of an X-ray applicator of the mobile X-ray unit having an indicator, according to a third embodiment of the present disclosure.

FIG. 5 a presents a schematic view of a phantom-based dosimetry system, according to embodiments of the present disclosure.

FIG. 5 b presents a cross-section of the phantom-based dosimetry system of FIG. 5 a, according to embodiments of the present disclosure.

FIG. 6 presents an end view of an X-ray tube, according to embodiments of the present disclosure.

FIG. 6, E-E presents a cross-section along line VII-E of the X-ray tube of FIG. 6, according to embodiments of the present disclosure.

FIG. 6, F-F presents a cross-section along line VII-F of the X-ray tube of FIG. 6, according to embodiments of the present disclosure.

FIG. 7 presents cross-sectional views of an exemplary dosimetry system for quality assurance, according to embodiments of the present disclosure.

FIG. 8 presents a flow chart illustrating an exemplary quality check process using the dosimetry system in FIG. 7, according to embodiments of the present disclosure.

FIG. 9 presents a flow chart illustrating an exemplary process to determine changes in surface dose rate and percentage depth dose as referenced in FIG. 8, according to embodiments of the present disclosure.

FIG. 10 presents a flow chart illustrating an exemplary process to determine flatness changes at multiple locations as referenced in FIG. 8, according to embodiments of the present disclosure.

FIG. 11 presents an exemplary quality check report, according to embodiments of the present disclosure.

DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings.

FIG. 1 a presents a perspective view of a mobile X-ray unit according to the present disclosure. The mobile X-ray unit 10 includes a base 2 having at least a high voltage supply unit, a cooling system, and a control unit (FIG. 2) for controlling operation of an X-ray applicator 4. The X-ray applicator 4 includes an X-ray tube (FIG. 3) disposed in an outer housing of the X-ray applicator 4. The X-ray applicator 4 may be connected to the base 2 using flexible cables 3, which may be at least partially disposed in a displaceable panel 5. The X-ray applicator 4 may be coupled to an articulated arm 4 a, which may include a pivot for varying the position and/or angle of the X-ray applicator 4 in space. The X-ray applicator 4 may include a longitudinal axis and an exit window 8 through which the generated X-ray beam 8 a may be emitted. The articulated arm 4 a may also be connected to the displaceable panel 5 to change a vertical position of the applicator 4. In some embodiments, the displaceable panel 5 may be provided with a handle 6 enabling easy manipulation thereof. The displaceable panel 5 may be guided along suitable rails for enabling a substantially smooth and shock-free displacement thereof.

In one embodiment, the X-ray applicator and the X-ray tube may be coaxially disposed. A longitudinal axis of an anode of the X-ray applicator may be substantially parallel to a longitudinal axis of the X-ray applicator so that the X-ray beam 8 a may propagate from the exit surface 8 having a beam axis 8 b substantially corresponding to a longitudinal axis of the X-ray tube.

In various embodiments of the present disclosure, a phantom-based dosimetry system may be provided so as to provide data on at least the percentage depth dose of the emitted X-ray field. As shown in FIG. 1, the dosimetry system may include a plurality of dose meters, such as 9 a, 9 b, 9 c, and 9 d. In some embodiments, a dose meter may be a device capable of generating on-line data may be provided. For example, Ionization chambers and solid state detectors such as semiconductor detectors may be suitable for this purpose. Some dose meters, such as 9 a and 9 b may be arranged on the surface of the phantom, while others, such as 9 c and 9 d, may be placed at specific depth (e.g., at 5 mm depth). By providing a plurality of point measurements, parameters such as, for example, the percentage depth dose and beam flatness may be determined. It will be appreciated that the dosimetry system may be operable to provide absolute data (absolute dosimetry) or relative data against a baseline (relative dosimetry). For both absolute dosimetry and relative dosimetry, a calibration may be carried out. For determining percentage depth dose a number of dose meters such as 9 c and 9 d (at least two) at specific depths on the central axis 8 b may be provided. For soft X-rays (50-130 kV) it may be sufficient to measure data at the surface and at 5 mm depth. It will be further appreciated that the set of dose meters may be as large as 10-20 or even up to 50 detectors. In order to prevent interference, the dose meters located on the surface (e.g., 9 a and 9 b) may be positioned outside the shadow of the respective dose meters located at the depth (e.g., 9 c and 9 d). In some embodiments, the signal from the dosimetry unit may be supplied into a control unit 21 of the mobile X-ray unit for on-line dose delivery control and/or to generate an interrupt signal.

In some embodiments, an indicator may be provided to position the X-ray applicator 4 with respective to the phantom-dosimetry system 9. The indicator may be used to delineate the X-ray field generated by the X-ray tube (FIG. 3) inside the X-ray applicator 4. In some embodiment, the indicator may be a light source, such as, for example, a light emitting diode, a laser, or the like.

The light source may be arranged either inside the X-ray applicator 4, or around the X-ray applicator 4, or it may be remotely positioned, for example in the base 2. In the latter case, light from the light from the light source (not shown) may be conducted towards the X-ray applicator 4 using one or more optical fibers. More details on suitable light source arrangements, although not limiting, are discussed with reference to FIGS. 4 a-4 c.

The displaceable panel 5 may include a display 7, which may function as a suitable user interface 7 a. For example, the patient data, such as a photo of the patient and/or a photo of a lesion may be provided in window 7 b, whereby relevant patient information, such as the date of birth, gender, dose prescription, and dose delivery protocol may be displayed in window 7 c. Buttons 7 d may be provided as touch functionality for enabling entering data. Additionally and/or alternatively, suitable hardware switches or buttons may be provided as well.

In some embodiments, the display 7 may be arranged as a touch-sensitive screen for enabling suitable data input into the system. For example, the display panel may comprise buttons or switches for switching the indicator (i.e., light source) on. Optionally, the indicator may always be on when the X-ray unit is switched on. The user interface may further be used to input a prescribed dose and, possibly, a prescribed dose distribution, especially when dose modifiers are used for providing a gradient in the dose profile across the X-ray field. The user interface may also be arranged to display data on actual dose delivery and dose distribution profile during the treatment. It will be appreciated that by using the phantom-based dosimetry system the dose delivery protocol may be compared with actual dose delivery data in real time and, if necessary, the actual dose delivery may be corrected in real time and/or during further sessions should a discrepancy in prescribed and delivered dose of more than 1% occur.

FIG. 1 b presents a partial perspective view of the mobile X-ray unit illustrating movement of the displaceable panel. In this enlarged view 10 a, specific elements of the displaceable panel 5 are depicted. A handle 6 may be implemented as a mechanical item for pulling or pushing the displaceable panel 5. Alternatively, the handle 6 may be arranged as an electrical actuator for triggering motors (not shown) for displacing the displaceable panel 5. For example, when the handle 6 is pulled the motors may be activated for causing the panel 5 to displace in a direction A. Pushing of the handle 6 may cause lowering of the panel 5 in a direction B. In some embodiments, the mobile X-ray unit 10 may include stops, limits, or other known structures for limiting the movement of the displaceable panel 5. This may be advantageous for ensuring mechanical stability of the mobile X-ray unit 10 (limitation of the upper level) and may also be beneficial for preventing cable damage (limitation of the lower level). In some embodiments, the displaceable panel 5 may travel along built-in rails whose length may be chosen for limiting the displacement range of the panel 5 in a desirable way.

FIG. 1 c illustrates the displacement of the X-ray applicator 4 of the X-ray unit 10. It will be understood that the mobile X-ray unit 10 may be configured so as to support a broad range of translational and rotational movements of the X-ray applicator 4.

In view 11, the X-ray applicator 4 is in a retracted position. It will be appreciated that cabling is not depicted for clarity reasons. The retracted position may be suitable for transport of the mobile X-ray unit 10 towards a booth and/or for maneuvering the X-ray unit 10 around the patient. In order to retract the X-ray applicator 4 as close as possible to the base 2, the articulated arm 4 a may be positioned under the outer portion 5 a of the displaceable panel 5. For ensuring stability of the mobile X-ray unit 10 during maneuvering thereof, a load block 2 a may be provided for lowering the point of gravity of the X-ray unit 10.

In view 12, the X-ray applicator 4 may be in an extended position (i.e., working position) having an X-ray exit surface 8 oriented towards a patient P. In order to suitably position the X-ray applicator 4 with respect to the patient P, the displaceable panel 5 may be moved to an intermediate position located between a lowest stand position and a highest stand position of the displaceable panel 5. The articulated arm 4 a may be used for suitably rotating the X-ray applicator 4 about a rotation axis. In one embodiment, a rotation axis is selected to coincide with a direction in which the X-ray beam is emitted from exit surface 8 for a vertically oriented X-ray applicator 4.

In view 13, the X-ray applicator 4 may be in a lowered position. For this purpose the displaceable panel 5 may be in its lowest position and the arm 4 a may be used for orienting the X-ray applicator 4 in a desirable way.

FIG. 2 is a diagrammatic representation of the mobile X-ray unit 10 according to embodiments of the disclosure. The mobile X-ray unit 10 may include a high voltage supply, preferably adapted to generate 50-75 kV X-rays in a suitable X-ray tube, a cooling system 21 d for cooling the X-ray tube during use, and a control system 21 for controlling electronic and electric parameters of sub-units of the X-ray unit during use. View 20 diagrammatically depicts main units of the control system 21 and of the X-ray applicator 22.

The control system 21 may include a hard wired user interface 21 a for enabling a user to switch on and switch off of the high voltage supply 21 b. In some embodiments, the high voltage supply 21 b includes a high voltage generator 21 c with improved ramp-up and ramp-down characteristics. The high voltage supply may be operable to deliver power of about 200 W in use. In some embodiments, the ramp-up time may be of the order of 100 ms. The hard wired interface 21 a, may also be arranged to automatically switch on the cooling system 21 d when the high voltage generator 21 c is switched on. In addition, the control system 21 may include a primary controller 21 e arranged for controlling the dose delivery from the X-ray applicator 22. The primary controller 21 e may be provided with a primary counter adapted to register time lapsed after the X-ray radiation is initiated. The primary counter may then automatically switch off the high voltage supply 21 b to the X-ray tube 22 a in the event a pre-determined dose is reached. It will be appreciated that the pre-determined dose is at least dependent on the energy of the X-rays and the dose rate, which may be calibrated in advance. Where calibrated data is made available to the primary controller 21 e, adequate primary dose delivery control may be achieved. In some embodiments, a secondary controller 21 f may be provided for enabling an independent loop of dose delivery control. The secondary controller 21 f may be connected to a dose meter accommodated inside the X-ray applicator 22 in the X-ray field before the collimator 22 d. Accordingly, the dose meter may provide real-time data on actual dose delivery taking into account dose variation during ramp up and ramp down of the high voltage source. Still preferably, the control system 21 may include a safety controller 21 g adapted to compare readings from the primary controller 21 e and the secondary controller 21 g for switching off the high voltage generator 21 c after a desired dose is delivered. Additionally and/or alternatively, the safety controller 21 g may be wired to guard emergency stop, door interlock, and a generator interlock.

The control system 21 may further include a dosimetry control 21 h, configured to communicate with a phantom-based dosimetry system on-line. It is also possible that the dosimetry control 21 h may accept data from a scanned dosimetric field and update dose delivery data post-processing.

The dosimetry control 21 h may be arranged to provide an interrupt signal, should the real-time dose meter measure a substantial deviation between the prescribed dose and the measured dose. For example, the dosimetry control 21 h may provide a suitable interrupt signal to the high voltage generator control 21 c to switch off the high voltage generator 21 c.

The control system 21 may further include an indicator controller 211 for controlling an indicator (i.e., a light source) used to delineate at least a portion of the X-ray beam. In some embodiments, the indicator controller 211 may be linked to a power supply unit 21 b for switching on the light source once the system is on. Alternatively, the light source may be switched on demand. Accordingly, the indicator controller 211 may be arranged to provide electrical power to the light source when triggered by the user. The user may provide a suitable trigger signal by a user interface, or, for example, using a dedicated hardware switch.

The X-ray applicator 22 may include an X-ray tube 22 a housed in an outer housing (shielding) 22 k. In the exemplary embodiment, a target element, a collimator 22 d, and an exit window of an X-ray tube 22 a may be in parallel so that the generated X-ray beam may be propagated substantially parallel to a longitudinal axis of the X-ray tube 22 a. The X-ray tube 22 a may have a target element-collimator distance of between 4 and 10 cm, and preferably 5 and 6 cm. The X-ray applicator 22 may further include a beam hardening filter 22 b selected to intercept low-energy radiation and a beam flattening filter 22 c, designed to intercept portions of X-ray radiation for generating a substantially flat beam profile near the exit surface of the X-ray applicator 22. Further, the X-ray applicator 22 may include one or more collimators 22 d arranged to define the shape of the X-ray beam. In some embodiments, a set of collimators 22 d may be used having, for example, diameters of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, and 5 cm. It will be appreciated that although circular collimators are discussed, collimators of any shape, such as square, elliptic, or custom made collimators are possible. It may be advantageous to have an X-ray applicator 22 with automatic collimator detection device 22 f configured to automatically signal which collimator is being used. In some embodiments, resistive sensing may be used to identify which collimator 22 d is being used. In particular, each collimator may be provided with at least a couple of projections for bridging a resistive path provided in a collimator receptacle (FIG. 5). The resulting electrical resistance of the receptacle constitutes a signal representative of a collimator being used.

The X-ray applicator 22 may also include a built-in temperature sensor 22 g adapted to monitor a temperature of the X-ray tube 22 a and/or its shielding 22 k. The signal from the temperature sensor 22 g may be received by the control system 21 which may carry out the analysis thereof. Should the measured temperature be elevated beyond an allowable level, an alarm signal may be generated. Optionally, a shut-off signal to the high voltage generator may be provided. The X-ray applicator 22 may further include a radiation sensor 22 h arranged inside the outer housing 22 k for detecting X-ray radiation which may be delivered by the X-ray tube 22 a. Preferably, for safety reasons the X-ray applicator 22 may include a non-volatile data storage 22 i arranged for recording operational parameters of at least the X-ray tube 22 a. Further, to enhance radiation safety, the X-ray applicator 22 may be provided with a radiation indicator 22 j arranged for providing a visual and/or an audio output to the user and/or the patient regarding ON/OFF condition of the X-ray tube 22 a. It will be appreciated that the radiation indicator 22 j may include a plurality of signaling devices. In one embodiment, at least one signaling device, for example a light emitting diode (LED), may be associated with the X-ray applicator 22 and provided on the X-ray applicator 22. It is understood, however, that the signaling devices may be positioned at any other location on the mobile X-ray unit.

FIG. 3 presents a schematic view of a phantom-based dosimetry system of the mobile X-ray unit. The phantom-based dosimetry system 100 may be adapted to be positioned at a distance with respect to the X-ray applicator 4, as is representative for patient treatments (e.g., 0.5-2 cm). However, it is contemplated that the dosimetry system may be positioned at a distance of up to 10 cm. The phantom-based dosimetry system may be used to obtain dosimetry data for all representative distances between the X-ray applicator 4 and the phantom Ph. It will be appreciated that although the phantom Ph is shown as a flat structure, the phantom Ph may have a shape corresponding to a non-flat surface on a human body or an external organ. Such phantom may be referred to as a humanoid phantom. In those embodiments, the humanoid phantom may have a Z value corresponding to that of a human soft tissue.

In order to align the phantom Ph with respect to the X-applicator 4, the phantom Ph may be provided with an alignment mechanism, and the X-ray applicator may be provided with an indicator for visualizing the X-ray beam. It may be sufficient, however, to visualize only a central ray of the X-ray beam 8 a, using a laser, for example.

The X-ray applicator 4 discussed above may include an X-ray tube arranged with an anode 1 having a target element 1 a for generating a diverging X-ray beam 8 a. The target element 1 a may be a substantially flat plate which may extend substantially perpendicular to a longitudinal axis of the anode 1. In one embodiment, the anode 1 may be aligned along axis 8 b of the X-ray beam (and the X-ray tube), however, it is understood that other respective orientations are possible. The X-ray beam 8 b may be emitted from an exit surface 8′ of the X-ray applicator. It will be appreciated that suitable filters, a collimator, and an exit window of the X-ray tube are not depicted for clarity reasons. Accordingly, the exit surface 8′ does not necessarily correspond to the exit window of the X-ray tube.

In one embodiment, an indicator such as, for example, a light source, may be used to position the X-ray applicator 4 with respect to the phantom-based dosimetry. In one embodiment, the indicator may include two light sources 15 a, 15 b configured to generate a narrow beam light. In this embodiment, the light sources 15 a, 15 b may be mounted on respective support arms 16 a, 16 b on an outer surface of the X-ray applicator 4. The light sources 15 a, 15 b may be configured to provide a light beam that intersects at a point in space C corresponding to the beam axis 8 b. The phantom-based dosimetry system Ph may then be centralized with respect to the point C for intercepting the X-ray beam.

In order to obtain percentage depth dose data, the phantom Ph may be provided with a plurality of dose meters distributed within its volume. For example, a number of dosimetric films may be provided across the X-ray field at characteristic depths such as, for example, 5 mm, 1 cm, and 5 cm. Such transversal films may also be used to examine beam flatness at specified depths. Alternatively, a dosimetric film extending in a vertical plane of the phantom Ph and running through a central axis 8 b may be provided. Such an arrangement may be used to provide continuous depth dose data. It will be appreciated that the phantom Ph may be used in a great variety of ways cooperating with a plurality of radiation detectors which are may be available to carry out dosimetry of soft X-rays. Those skilled in the art will readily appreciate corresponding embodiments of the phantom P.

The phantom-based dosimetry system 100 may be connected to the dosimetry control unit 21 h by cables 19. It will be appreciated that the cables 19 may be used in combination with an electronic dose meter, such as an ionization chamber or a semiconductor detector.

Although the phantom-based dosimetry system of the present disclosure is discussed with reference to the X-ray applicator provided with an indicator (e.g., a light source), it will be appreciated that the phantom-based dosimetry system may be practiced without an indicator delineating the X-ray field.

FIG. 4 a presents a cross-section of an X-ray applicator of the mobile X-ray unit having an indicator, in accordance with a first embodiment of the present disclosure. The X-ray applicator 30 includes an outer housing 36 and an X-ray tube 35 disposed in the outer housing 36. The X-ray tube 35 may have an external shielding 35 a, a target element (not shown), and a collimator 33.

In one embodiment, the indicator may be light source 48 a. The light source 48 may cooperating with a mirror 48 for emitting a light beam indicative of a two-dimensional beam of X-rays produced by the X-ray tube 35. In some embodiments, X-rays may have a propagation axis 45 a which coincides with a longitudinal axis of the X-ray tube 35. The light source 48 a and the mirror 48 may be arranged so that the light beam may substantially propagate along the longitudinal axis of the X-ray tube 45 a.

When the light beam is intercepted by a collimator 33 a visual indication and simulation of the two-dimensional X-ray beam is created. In one embodiment, the distance between a target element of the anode (not shown) and the collimator 33 is in the range of 4 to 10 cm, preferably about 5 to 6 cm. Such relatively short target element-collimator distance may generate an X-ray beam having a substantially narrow penumbra (1.5-1.8 mm for 20/80% lines) and good beam flatness due to a relatively small focal size.

The X-ray applicator 30 may further include a filter 39 for hardening the X-ray beam generated at the target element, a beam flattening filter 40 for flattening out a beam profile, and a collimator receptacle 41 for receiving collimator 33.

A cooling system 34 may be provided so as to prevent overheating of the X-ray tube 35. In one embodiment, the cooling system 34 may be arranged in the space between the X-ray tube 35 and the shielding 35 a in contact with the surface of the X-ray tube 35. A suitable coolant may be provided using a pipe 31. It is contemplated that the coolant may be water, a pressurized gas, or even special oil. The X-ray applicator 30 may further include a temperature sensor 37.

The X-ray assembly 30 may further include a suitable radiation detector 38 connected to a radiation indicator 43. Data collected by the radiation detector 38 may be stored in a data storage unit 44.

In order to protect the X-ray exit surface (including window) of the X-ray applicator 30 from intra-patient contamination, an applicator cap 42 may be provided to cover at least the exit surface of the X-ray applicator 30. In some embodiments, the applicator cap 42 is thick enough to fully intercept secondary electrons emanating from the X-ray applicator 30. The applicator cap 32 may be manufactured from PVDF (polyvinylidene fluoride) and may be about 0.4-0.7 mm, and preferably 0.6 mm thick across the window portion. The applicator cap may have density of about 1.75-1.8, and preferably 1.78. Alternatively the applicator cap 42 may be 0.3-0.6 mm thick, and preferably 0.5 mm thick across the window portion. In those embodiments, the applicator cap 32 may have a density of 1.30-1.45, and preferably 1.39. Further, the applicator cap 42 may be manufactured from PPSU (polyphenylsulfone). These materials may be particularly suitable as they as stable under influence of the X-rays and are suitable for different types of sterilization procedures, such as chemical sterilization, or sterilization under elevated temperatures.

FIG. 4 b presents a cross-section of an X-ray applicator of the mobile X-ray unit having an indicator, in accordance with a second embodiment of the present disclosure. In this exemplary embodiment, the indicator includes at least one optical fiber 47 a connected to a light source that may be positioned remotely in, for example, base 2.

Optical fiber 47 a may be provided in the collimator receptacle 41 above the collimator 33. The optical fiber 47 a may be configured to generate a light field that is substantially centered about the collimator opening 33 for creating a two-dimensional cross-section of an X-ray beam emitted from the collimator 33. In this embodiment, optical fiber 47 a may be configured to emit a substantially narrow beam having a divergence of the expected divergence of the X-ray beam.

Alternatively, it may be possible to use the optical fiber 47 a for visualizing a central axis 45 a of the X-ray beam in addition to visualizing the two-dimensional area of the X-ray beam. In this case, the optical fiber may be arranged to emit a narrow beam light producing a miniature light spot on a surface of the patient. In one embodiment, a dimension of the light spot is less than 5 mm², and more preferably a dimension of the light spot is about 1 mm². A suitable light emitting diode or a laser may be used for generating light emitted from the fiber 47 a. In one embodiment, the light emitting diode and the laser are remotely arranged with respect to the X-ray applicator 30. It will be appreciated that an alternative configuration may be used such as for example, having one or more light sources that may be electrically connected to one or more optical fibers.

FIG. 4 c presents a cross-section of an X-ray applicator 30 of the mobile X-ray unit having an indicator in accordance with a third embodiment of the present disclosure. In this exemplary embodiment, the indicator may be disposed externally of the X-ray applicator 30 and may be one or more light sources 52.

As illustrated in FIG. 4 c, the X-ray applicator 30 may include an anode 45 provided with a target element for generating an X-ray beam 45 c having a longitudinal X-ray axis 45 a. The one or more light source 52 may be configured to illuminate the longitudinal axis 45 a of the X-ray beam 45 c at a pre-determined distance D from the lower surface 49 of the X-ray applicator 30. It will be appreciated that the lower surface 49 may relate to the exit surface as discussed with reference to FIG. 1 a, or it may relate to the applicator cap, as will be discussed with reference to FIG. 5.

The one or more light sources 52 a, 52 b may be disposed on support arms 54 a, 54 b. Light sources 52 a, 52 b may generate narrow light beams 53 a, 53 b that may be directed towards the axis 45 a and intersect at a pre-determined distance D from the lower surface 49 of the X-ray applicator 30. Preferably, the distance D is selected to be between 0.5 and 2 cm. The support arms 54 a, 54 b may be arranged so that light beams 53 a, 53 b do not intersect the X-ray applicator 30.

In use, a user may position the X-ray applicator 30 with respect to the patient P in such a way that the beams 53 a, 53 b intersect at the surface of the patient. However, should the treatment regime require the use of a dose build-up material, the beams 53 a, 53 b may cross on a surface of the dose build-up material. In some embodiments, the support arms 54 a, 54 b may be adjustable to indicate the central axis 45 a at different distances from the lower surface 49 of the X-ray applicator 30. In order to calibrate adjustment of the support arms, a transparent calibration phantom may be used, wherein the central axis and depth are marked.

It will be appreciated that although FIGS. 4 a-4 c disclose separate embodiments of the indicator, a combination of such embodiments is contemplated as well. For example, embodiments directed to indicating the central axis may be combined with embodiments directed to indicating the complete field. In addition, internal and external indicators may be combined.

FIG. 5 a presents a schematic view of a phantom-based dosimetry system, according to embodiments of the present disclosure. As illustrated in FIG. 5 a, the X-ray applicator 4 and the phantom-based dosimetry system may be in a fixed configuration 60. For example, the phantom-based dosimetry system 61 may be screwed, clicked, slided, welded, or otherwise affixed to the X-ray applicator 4. In one embodiment, the phantom-based dosimetry system 61 includes a handle 62 for handling the components. The X-ray applicator 4 or the phantom-based dosimetry system 61 may be provided with a body 64 receiving a number of screws 67 a, 67 b so as to firmly attach the phantom-based dosimetry system 61 to the X-ray applicator 4. The body 63 of the phantom-based dosimetry system 61 may be manufactured from a plastic material, or, preferably, from a tissue equivalent material.

It may be advantageous to provide the phantom-based dosimetry system 61 which can be attached to the X-ray applicator 4, as suitable dosimetric measurements may be carried out for different angulations of the X-ray applicator 4.

FIG. 5 b presents a cross-section of the phantom-based dosimetry system of FIG. 5 a. As follows from FIG. 5 a, the X-ray applicator 4 may deliver an X-ray beam having an X-ray radiation 8 a, which may impinge on the phantom-based dosimetry system 61. It will be appreciated that the phantom-based dosimetry system 61 may include a background material 63 and a similar or a different material 66 used to accommodate a number of detector elements. For example, a PCB material may be used for accommodating the radiation detectors.

The radiation detectors provided in the phantom-based dosimetry system 61 may be configured to provide a signal representative of the measured radiation dose. For example, the background material 63 may include a transmitter 68 electrically connected to the detectors and configured to wirelessly transmitting read-out signals. It will be appreciated that the transmitter 68 may be provided at any desirable place on or inside the phantom, preferably outside the area irradiated by the X-ray beam. Alternatively, the phantom may be provided with an electronic device, which may be connected using suitable cables to an external data acquisition or data processing unit. Those skilled in the art will readily appreciate how to implement the described embodiments of the data communication unit.

FIGS. 6, 6E-E, and 6F-F, illustrate various views of the X-ray tube. The X-ray tube 100 may have a body 102 enclosing at one exit window 104 through which the X-rays pass. See FIG. 6, cross-section E-E. The exit window 104 may be made from a thin sheet of Beryllium metal. An applicator cap 106 may be positioned over the exit window 104 so as to covering the exit window 104 and protect exit window 104. Applicator cap 106 may be made from a plastic material. The applicator cap may be manufactured from PVDF (polyvinylidene fluoride) and has a thickness of about 0.4-0.7 mm, and preferably 0.6 mm, across the window portion. Alternatively, the applicator cap 106 may be manufactured from PPSU (polyphenylsulfone) and have a thickness of about 0.3-0.6 mm, and preferably 0.5 mm, across the window portion.

In the tube body 102, a target element 108 may be located at a range between 4 and 10 cm from the collimator 130, and preferably between 4 and 5 cm from the collimator 130 (see FIG. 6, cross-section F-F). It will be appreciated that this distance is measured between the outer surface of the target element 108 and a midplane of the collimator 130. The target element 108 may be made from Tungsten metal to provide the desired X-ray spectrum. The tungsten tip of the target element 108 may be mounted on a large anode assembly 110 which also serves to dissipate the heat created from the generation of the X-rays in the target element 108. Most of the anode assembly 110 is made from copper. The cathode 112 (see FIG. 6, cross-section F-F) may be located slightly off-axis near the exit window 104. Electrons emitted from the cathode are accelerated across the gap by the potential difference between the cathode and anode, in this case set at about 70 kV, to the target element 108 where the impact causes the generation of X-rays in a known manner. X-rays emitted from the target element 108 pass through a beam hardening filter 122 before passing through a collimator 130 and an exit surface 124 on an applicator cap 106. The collimator 130 may be housed in a suitable collimator receptacle 128.

The anode assembly 110 may be mounted in the body 102 and electrically insulated. One of a number of known techniques and materials may be used to provide the desired level of insulation between the anode assembly 110 and the body 102.

As is well known in the art, the production of X-rays generates a large amount of heat. Accordingly, it may be necessary to cool the X-ray tube 100 in order to maintain it at a safe temperature. Various cooling mechanisms are known and used in the art. In one embodiment, the X-ray tube 100 may be cooled by cooled water forced around the anode region. Cooled water enters the back of the tube by a first conduit 116 and leaves by a second conduit 118 (see FIG. 6, cross-section F-F). The water cooling circuit is a closed loop circuit, with the water leaving the tube assembly 105 to be cooled by a remote cooler (not shown) before returning to the X-ray tube 100. It is contemplated that oil or another liquid may be used as the cooling medium. It is also known that a pressurized gas may be used as an effective coolant in some applications.

As is known in the art, X-rays are generated and emitted in all directions, however the body 102 of the X-ray tube 100 and other internal components will tend to reduce the amount of radiation emitted from the body 102 of the X-ray tube 100 to a minimum, with most of the radiation emitted from the exit window 104. The thickness of the shielding provided by the body 102 may be designed so that it provides at least the minimum level of shielding required for safe use by the operator.

A high voltage cable assembly 120 may be connected to the anode assembly 110. The high voltage cable assembly 120 may be connected to flexible cable means (not shown), which in turn may be connected to a high voltage power supply.

A radiation detector 114 may be placed outside the path of the X-ray beam emitted from the target element 108 and passing through the exit window 104. This detector can be any known form of radiation detector. In one embodiment, the radiation detector may be a hardened semi-conductor connected to an amplifier. The radiation detector 114 may detect when the tube 102 is working and emitting X-ray energy. Output from the detector 114 may connected to a control unit, and the output signals from the detector 114 may be used to provide an optical indication to a user of whether the tube is operating or not. By this means an X-ray detector 114 may be provided which may be used to detect if the X-ray tube is on or off.

With further calibration of the radiation detector 114, it may be possible to determine and calculate the X-ray dose administered to the patient during the treatment. In this manner, it may be possible to have a real time dosimetry measurement system, in which the precise amount of radiation dose administered can be determined. Once the dose rate is known, a treatment plan can be modified during treatment. This may be advantageous because it may enable a very accurate and carefully controlled dose of X-rays to be administered.

In order to enable the X-ray tube 100 to be placed accurately over a tumour, a tumour illumination device may be is used. The tumour illumination device may include a plurality of lights 126 placed around the circumference of the X-ray tube 100 near the exit window 104. When in use, the lights shine onto the skin of the patient. Since the lights 126 are positioned around the circumference of the tube body 102, at a short distance from the end of the X-ray tube 100, they create a circle of light with a sharp cut off of the inner part of the circle. In this way, the position of the lights on the tube body 102 may create a shadow. This shadow circle may be used to indicate the region which will be subject to irradiation when the X-ray tube 100 is turned on. It should be appreciated the area within the circle may not be completely dark; the ambient light may be able to enter the shadow region.

In some embodiments, the lights 126 are white LEDs which can be bright enough to clearly illuminate the target element region but do not generate large amounts of heat and have very long lives. The lack of heat generation is important because the lights will be in close proximity to the skin of the patient, and so it is important to minimize the risk of burning or other damage to the skin. Other colors of LEDs may be used. Alternatively, other light sources could be used, such as known filament lamps or even a remote light source connected to the ring by fiber optic cables.

FIG. 7 presents cross-sectional views of an exemplary dosimetry system 200 for quality assurance (QA), according to embodiments of the present disclosure. QA dosimetry system 200 may be an exemplary embodiment of the dosimetry system in FIG. 1, used to perform a daily quality check for radiation dose, dose profile, and timing.

In some embodiments, QA dosimetry system 200 may have a number of dose meters positioned on surfaces at different depths. For example, FIG. 7 shows a QA dosimetry system 200 that has 26 dose meters, 13 (dose meters [0] through [12]) positioned on surface 200A located approximately 60 mm from the light spot and the other 13 (dose meters [13] through [25]) positioned on surface 200B located approximately 5 mm apart from surface 200A. As will be appreciated, the distance between the light spot and surface 200A is substantially the same as the distance between the light spot and a patient's skin. In some embodiments, the 5 mm thick space between surface 200A and surface B may be filled with materials such as PCB and solid water. In some embodiments, another layer of solid water may be placed below surface 200B.

Consistent with some embodiments, the dose meters may be arranged in a way that each can receive one or more signals without interference from others. Accordingly, dose meters [13] through [25] on surface 200B may be placed out of the radiation shade of dose meters [0] through [12]. For example, all the dose meters may be positioned in concentric circles in the X-ray beam on their respective surfaces, as shown in FIG. 7.

FIG. 8 presents a flow chart illustrating an exemplary quality check process 300 using dosimetry system 200 described in FIG. 7, according to embodiments of the present disclosure. Quality check process 300 may be performed at a predetermined frequency, such as daily, weekly, or whenever desired by the user, such as before each use of the mobile X-ray unit. Steps of quality check process 300 may be performed by QA dosimetry system 200, dosimetry control 21 h, or the combination thereof.

In Step 302, QA dosimetry system 200 may measure a radiation duration. In some embodiments, the radiation duration may be measured as the time lapse between start of radiation to the when dose meter [6] detects radiation. Typically, the radiation duration is approximately 65 seconds.

In Step 304, dosimetry control 21 h may determine changes in surface dose rate based on measurements acquired by QA dosimetry system 200. As used herein, a “surface dose rate” refers to the accumulated dose rate on surface 200A, measured by dose meters [0] through [12]. The surface dose rate may be an absolute dose rate, or a relative dose rate determined relative to a baseline dose rate. The change in surface dose rate may be determined as a relative difference between the surface dose rate and its baseline value.

In Step 306, dosimetry control 21 h may determine changes in percentage depth dose based on measurements acquired by QA dosimetry system 200. As used herein, a “percentage depth dose” (also known as PDD) refers to the accumulated dose rate on surface 200B, measured by dose meters [13] through [25]. Percentage depth dose essentially measures the absorbed dose deposited by a radiation beam into a medium as it varies with depth along the axis of the beam. Similar to the surface dose rate, the percentage depth dose may be an absolute dose, or a relative dose determined relative to a baseline dose rate.

FIG. 9 presents a flow chart illustrating an exemplary process 400 to determine changes in surface dose rate and percentage depth dose as referenced in Steps 304 and 306 of FIG. 8, according to embodiments of the present disclosure.

In Step 410, QA dosimetry system 200 and dosimetry control 21 h may measure and calculate sensor values for each dose meter, based on respective un-radiated values and radiated values. In some embodiments, QA dosimetry system 200 may measure the un-radiated value multiple times (e.g., 10 times) at a particular dose meter and average the measurements to obtain the averaged un-radiated value for the dose meter. This may be repeated for all dose meters [0] through [25] on surfaces 200A and 200B. Similarly, QA dosimetry system 200 may also measure an averaged radiated value for each dose meter as an average of multiple measures, and repeat it for all dose meters. In some embodiments, the sensor value for a dose meter is then calculated as the difference between the averaged radiated value and the averaged un-radiated value. As a result, sensor values S[0] through S[25] for dose meters [0] through [25] may be obtained.

In Step 420, baseline sensor values may be established for all the dose meters. In some embodiments, sensor values obtained during a very first quality check process may be stored as baseline sensor values. Baseline sensor values for dose meters [0] through [25] are referred to as B[0] through B[25].

In Step 430, dosimetry control 21 h may calculate summations of sensor values obtained in Step 420. In some embodiments, summations of sensor values may be calculated for surfaces 200A and 200B, respectively. In some embodiments, summations of baseline sensor values may be calculated for the two surfaces as well, as shown, for example below.

SumTop=Sum(S[0] . . . S[12])

SumBottom=Sum(S[13] . . . S[25])

SumBaselineTop=Sum(B[0] . . . B[12])

SumBaselineBottom=Sum(B[12] . . . B[25])

In Step 440, dosimetry control 21 h may calculate change ratios for the surface layer (e.g., surface 200A) and the bottom layer (e.g., surface 200B) based on the summations obtained in Step 430. As used herein, a “change ratio” is a ratio between a summation of sensor values and a summation of the corresponding baseline sensor values. For example, change ratios for surfaces 200A and 200B may be calculated as follows:

TopRatio=SumTop/SumBaselineTop

Bottom Ratio=SumBottom/SumBaselineBottom

In Step 450, dosimetry control 21 h may determine changes in surface dose rate based on the change ratio for the surface layer. For example,

SurfaceDoseRateChange=100*(TopRatio−1)

In Step 460, dosimetry control 21 h may determine changes in percentage depth dose based on the change ratios for the surface layer and bottom layer. For example,

PddChange=100*(BottomRatio/TopRatio−1)

Returning to FIG. 8, in Step 308, dosimetry control 21 h may determine flatness changes at multiple locations based on measurements acquired by QA dosimetry system 200. In some embodiments, the multiple locations may be selected to spread out evenly on the surface. For example, cardinal locations such as north, south, east, west, and the beam center may be selected. In some embodiments, the multiple locations may be selected based on the distribution of the dose meters.

FIG. 10 presents a flow chart illustrating an exemplary process 500 to determine flatness changes at multiple locations as referenced in FIG. 8, according to embodiments of the present disclosure. Steps 510-540 may be performed substantially the same as Steps 410-440 of process 400. Accordingly, descriptions of steps 510-540 are not repeated here. In Step 550, dosimetry control 21 h may calculate relative changes for each surface dose meter ([0] through [12]) based on the sensor value, the baseline sensor value of the corresponding dose meter, and the change ratio for the surface layer (surface 200A). For example, relative change C[i] for dose meter [i] on surface 200A is calculated as follows:

C[i]=100*(S[i]/B[i]/TopRatio−1)

Similarly, in Step 560, dosimetry control 21 h may calculate relative changes for each surface dose meter ([13] through [25]) based on the sensor value, the baseline sensor value of the corresponding dose meter, and the change ratio for the bottom layer (surface 200B). For example, relative change C[i] for dose meter [i] on surface 200B is calculated as follows:

C[i]=100*(S[i]/B[i]/BottomRatio−1)

In Step 570, dosimetry control 21 h may calculate flatness changes at multiple locations based on the relative changes of dose meters near each location. In some embodiments, flatness changes may be calculated in eight cardinal directions and the beam center. For each location, dose meters located on either surface 200A or surface 200B in a direction may be used to calculate the flatness change for that direction. For example, flatness changes may be calculated as follows:

NorthChange=Average(C[0]+C[13]+C[14]+C[15])

NEChange=Average(C[0]+C[2]+C[8]+C[15])

EastChange=Average(C[8]+C[15]+C[20]+C[25])

SEChange=Average(C[8]+C[11]+C[12]+C[25])

SouthChange=Average(C[12]+C[23]+C[14]+C[25])

SWChange=Average(C[4]+C[10]+C[12]+C[23])

WestChange=Average(C[4]+C[13]+C[18]+C[23])

NWChange=Average(C[0]+C[1]+C[4]+C[13])

CenterChange=Average(C[3]+C[5]+C[6]+C[7]+C[9]+C[16]+C[17]+C[19]+C[21]+C[22])

Returning to FIG. 8, in Step 310, the QA check results, including the parameters measured or determined in Steps 302-308, may be compared to a first set of pre-determined criteria. For example, the first set of pre-determined criteria may be set as follows:

Change in surface dose rate <2%, AND

Change in percentage depth dose <2%, AND

All flatness changes <2%, AND

radiation duration is within 1% of the planned radiation time

If all first criteria are met (Step 310: Yes), dosimetry control 21 h may determine that the quality check is passed (Step 312), and process 300 may proceed to Step 320. Otherwise, if the QA check results fail to meet any of the first criteria (Step 310: No), the QA check results may be compared to a second set of pre-determined criteria (Step 314). In some embodiments, the second set of criteria is less stringent than the first set of criteria. For example, the second set of pre-determined criteria may be set as follows:

Change in surface dose rate <3%, AND

Change in percentage depth dose <3%, AND

All flatness changes <3%, AND

radiation duration is within 1% of the planned radiation time

If the QA check results fail to meet any of the second criteria (Step 314: No), dosimetry control 21 h may determine that the quality check has failed (Step 316).

Otherwise, if all second criteria are met (Step 314: Yes), dosimetry control 21 h may determine that the quality check is tentatively passed but a warning should be provided to the user (Step 318). After Step 312, Step 316, or Step 318, process 300 may proceed to Step 320, where a quality check report is generated and provided to the user.

FIG. 11 presents an exemplary quality check report 600, according to embodiments of the present disclosure. As shown in FIG. 11, quality check report 600 may indicate the hardware used for the quality check, the measurements made during the quality check, and a flatness change map. Among the measurement results listed are planned fraction time, measured fraction time, change in surface dose rate relative to the baseline, change in percentage depth dose relative to the baseline. For example, in quality check report 600, the surface dose rate is 0.2% higher than the baseline, and the percentage depth dose is 0.2% lower than the baseline.

The flatness change map in quality check map 600 shows flatness changes at nine locations: the eight directions and the beam center. For example, the NorthChange is 1.5% relative to the baseline. Since the flatness changes are all within 3%, and both changes in surface dose rate and percentage depth dose are within 2%, the first set of criteria is met, and the quality check has passed (e.g., test result OK).

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It will be further appreciated that when a reference to an on-line dosimeter is made, a real-time functionality is contemplated as well. The descriptions above are intended to be illustrative, not limiting. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims. 

What is claimed is:
 1. A mobile X-ray unit comprising: an X-ray applicator for emitting an X-ray beam for irradiating an object; a phantom-based dosimetry system configured to perform a dosimetry check of the X-ray beam, the phantom-based dosimetry system including two sets of dose meters, each set being positioned on a surface at a distinct depth; and a dosimetry control unit configured to receive measurements from the two sets of dose meters and determine whether the dosimetry check is passed based on the measurements.
 2. The mobile X-ray unit according to claim 1, wherein the two sets of dose meters are positioned in concentric circles in the X-ray beam.
 3. The mobile X-ray unit according to claim 1, wherein the two sets of dose meters include a first set of dose meters positioned on the surface of the phantom-based dosimetry system and a second first of dose meters positioned at a pre-determined distance away from the surface.
 4. The mobile X-ray unit according to claim 3, wherein the second set of dose meters are positioned out of a radiation shade of the first set of dose meters.
 5. The mobile X-ray unit according to claim 1, wherein the phantom-based dosimetry system is calibrated to measure an absolute dosimetry or a relative dosimetry of a dose penetration.
 6. The mobile X-ray unit according to claim 1, wherein the dosimetry control unit is configured to determine one or more dosimetry parameters including at least one of a radiation duration, a change in surface dose rate, a change in percentage depth dose, or a plurality of flatness changes at a plurality of predetermined locations in the phantom-based dosimetry system.
 7. The mobile X-ray unit according to claim 6, wherein the dosimetry control unit is configured to compare the determined one or more dosimetry parameters with a first set of predetermined criteria.
 8. The mobile X-ray unit according to claim 7, wherein the dosimetry control unit is configured to compare the determined dosimetry parameters with a second set of predetermined criteria when the determined dosimetry parameters do not meet the first set of predetermined criteria, wherein the second set of predetermined criteria is less stringent than the first set of predetermined criteria.
 9. The mobile X-ray unit according to claim 6, wherein the change in surface dose rate is determined using a first set of dose meters positioned on the surface of the phantom-based dosimetry system, and the change in percentage depth dose is determined using a second set of dose meters positioned at a pre-determined distance away from the surface, wherein determining the change in surface dose rate or determining the change in percentage depth dose comprises: determining a sensor value and a baseline sensor value for each dose meter within the respective set of dose meters; determining an accumulated sensor value by summing up the sensor values and an accumulated baseline sensor value by summing up the baseline sensor values; and determining the change in surface dose rate or the change in percentage depth dose as the difference between the accumulated sensor value and the accumulated baseline sensor value.
 10. The mobile X-ray unit according to claim 6, wherein the plurality of predetermined locations include at least one cardinal directions and an X-ray beam center.
 11. The mobile X-ray unit according to claim 6, wherein the each flatness changes is determined based on relative dose changes measured by dose meters in the neighborhood of the corresponding predetermined location.
 12. The mobile X-ray unit according to claim 6, wherein the dosimetry control unit is configured to generate a dosimetry check report indicating whether the dosimetry check is passed, wherein the dosimetry check report includes a graphic view of the plurality of flatness changes.
 13. A method for performing a dosimetry check using a phantom-based dosimetry system in a mobile X-ray unit, the phantom-based dosimetry system including two sets of dose meters, including a first set of dose meters positioned on a surface at a first depth and a second a set of dose meters positioned on a surface at a second depth, the method comprising: measuring a plurality of dosimetry parameters using the two sets of dose meters, including a first dosimetry parameter indicative of a change of dose at the first depth and a second dosimetry parameter indicative of a change of dose at the second depth; and determining whether the dosimetry check is passed based on the dosimetry parameters.
 14. The method according to claim 13, wherein the plurality of dosimetry parameters include at least one of a radiation duration, a change in surface dose rate, a change in percentage depth dose, or a plurality of flatness changes at a plurality of predetermined locations in the phantom-based dosimetry system.
 15. The method according to claim 14, further comprising comparing the plurality of dosimetry parameters with a first set of predetermined criteria.
 16. The method according to claim 15, further comprising comparing the plurality of dosimetry parameters with a second set of predetermined criteria when the plurality of dosimetry parameters do not meet the first set of predetermined criteria, wherein the second set of predetermined criteria is less stringent than the first set of predetermined criteria.
 17. The method according to claim 14, wherein the change in surface dose rate is determined using the first set of dose meters, and the change in percentage depth dose is determined using the second set of dose meters, wherein determining the change in surface dose rate or determining the change in percentage depth dose comprises: determining a sensor value and a baseline sensor value for each dose meter within the respective set of dose meters; determining an accumulated sensor value by summing up the sensor values and an accumulated baseline sensor value by summing up the baseline sensor values; and determining the change in surface dose rate or the change in percentage depth dose as the difference between the accumulated sensor value and the accumulated baseline sensor value.
 18. The method according to claim 14, wherein the plurality of predetermined locations include at least one cardinal directions and an X-ray beam center.
 19. The method according to claim 14, wherein the each flatness changes is determined based on relative dose changes measured by dose meters in the neighborhood of the corresponding predetermined location.
 20. The method according to claim 14, further comprising generating a dosimetry check report indicating whether the dosimetry check is passed, wherein the dosimetry check report includes a graphic view of the plurality of flatness changes. 